8 September 2010 Reliable metallic tape connection on CIGS solar cells by ultrasonic bonding
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Abstract
Metallic tapes are used to reliably connect CIGS thin-film solar panels to the junction box. Compared to soldering and gluing, ultrasonically bonding these tapes offers several benefits: a room-temperature process, lower consumable cost, stronger and more reliable bonds, and lower contact resistance. A MoSe2 layer can form on the back contact Mo layer during the CIGS selenization. The thickness of the MoSe2 layer varies with the details of the deposition and selenization process. MoSe2 is a solid lubricant that creates a low friction interface between the tape and Mo layer, thus reducing ultrasonic coupling and making ultrasonic bonding more challenging. MoSe2 also has a volume resistivity about 3,500 times higher than Mo. Its presence increases the tape contact resistance and thus reduces the efficiency of the solar module. It is therefore desired to remove the MoSe2 layer to make a reliable connection. Several processes were investigated on samples with varying MoSe2 layer thickness. The effectiveness of those processes was studied and evaluated by using Scanning Electron Microscope (SEM), Energy Dispersive X-ray Analysis (EDAX), 90° bond peel test, and electrical contact resistance measurements. Complete removal of the MoSe2 layer without damaging the Mo layer underneath was successfully achieved. Strong bonds with more than 900g peel force for 2.00mm (width) × 0.10mm (thickness) Aluminum tapes and a low contact resistivity of <1.5 mΩcm2 were consistently demonstrated.
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Tao Xu, Orlando Valentin, Christoph Luechinger, "Reliable metallic tape connection on CIGS solar cells by ultrasonic bonding", Proc. SPIE 7771, Thin Film Solar Technology II, 77710R (8 September 2010); doi: 10.1117/12.860962; https://doi.org/10.1117/12.860962
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